In high speed connectionless networks such as packet transmission networks, or other networks not using dedicated transmission facilities, high traffic loads often result in extensive delays between packet transmissions. Such delays can actually decrease the overall throughput of the network. This phenomenon is known as congestion. Data packets arriving at a switching node in a congested system find no available buffer space and hence must be discarded and retransmitted at a later time. Such discard and retransmission, in turn, further increases the traffic load on the system, causing the congestion condition to further degenerate. Increased geographic separation of the ports on the network increases round trip delay of messages on the network, further accentuating the congestion control problem. Moreover, even on shorter round trips, large bandwidths increase the number of packets in transit, also accentuating the congestion control problem.
Traffic management systems are designed to either avoid traffic congestion or to control such congestion once it has come into existence. It has become common to provide so-called "end-to-end" congestion control. That is, traffic is observed at either the entry point, the exit point, or both, and the rate of transmission adjusted to prevent congestion. While such a strategy may be appropriate for connection-oriented networks, where a connection is set up between the sending and the receiving ports prior to the exchange of messages, such a strategy is not effective for connectionless networks where data packets are switched locally at switching nodes in response to information in the data packet itself. In addition, connection-oriented networks, having at least some transmission facilities exclusively used by a connection, are extremely inefficient for transmitting bursty computer network traffic due to the large overhead cost of setting up the connection and the short holding time for such a connection. Thus, end-to-end congestion control techniques which are viable in connection-oriented networks are not well-suited to connectionless packet networks.